A Records
A records point to IP addresses.
The A records are responsible for mapping requests for the domain name to the IP Address of the web server which is responsible for the domain name. Each hostname, or subdomain, may have a different IP Address associated with it.
For Example: The nameservers for Misk.com will direct all requests for www.misk.com and misk.com to the web server at 64.74.251.51, while requests for webmail.misk.com are directed to 64.74.251.25.
CNAME Record
CNAME records are aliases that point to another Hostname.
The benefit to using CNAME records is that if an IP Address changes you do not have to update your CNAME Record. The IP Address would only have to be updated on the Hostname that you are pointing to.
CNAME records can also be used in conjunction with a Dynamic DNS service for users with a dynamic IP Address which may change from time to time. Requests for the domain name will need to be directed to the to the Hostname provided by the Dynamic DNS server. Your Dynamic DNS service will keep track of the current IP Address for your server and will they will update their records so you will not have to make any changes to your domain name itself.
MX Records
MX or Mail eXchange records handle email for your domain.
The MX Record directs all of the emails sent to addresses on your domain name to your mail server where you can then retrieve them.
TTL
TTL or Time To Live lets other DNS servers know how often to check back for changes.
Note: Setting an extremely low value will not cause DNS changes to be propagated sooner. TTL is a MINIMUM value and the ISP will not update their records any quicker then their minimum update times.
Subdomains
Subdomains are offshoots of a domain.
For Example: webmail.misk.com is a subdomain of misk.com which points to our webmail server.
What does the "@" symbol represent?
The "@" symbol represents the root.
The root is the base level of your domain name without any subdomain attached to it.
For Example: Requests for Misk.com would be handled by the root record with the root record with the "@" sign, while requests for www.misk.com would be handled by the "www" record.
What does the "*" symbol represent?
The "*" symbol is used to create Wildcard entries.
Wildcards direct all traffic that isn't otherwise specified to a single place. A DNS wildcard will take any subdomain (except those that already exist).
For Example: ww.misk.com (and any other subdomains we have not specifically setup) will automatically redirect to www.misk.com, but webmail.misk.com which we have setup will point to our webmail server.